Heat sealable coated textile fabric for inflatable vehicle restraint systems and method for producing same

ABSTRACT

A coated textile fabric is disclosed for manufacturing an air holding device for a vehicle restraint system, including a base woven, knitted or non-woven base textile fabric having a first surface and a second surface. The base textile fabric is completely or partially coated with an adhesive polyurethane to form a first coating layer, the first coating layer being coated with a second composite coating layer. The second composite coating layer is preferably a polyurethane, a polysiloxane, and an epoxy resin which acts as a filler and adhesion promoter. A third coating layer is formed of a polymeric polyurethane material coated on the second composite layer. A method of producing the coated textile fabric is also disclosed. A heat sealing die for forming sealing beads to seal such coated textile fabrics to form air holding devices is also disclosed.

RELATED APPLICATIONS

This is a divisional of U.S. Ser. No. 09/452,030, filed Nov. 30, 1999now U.S. Pat. No. 6,350,709, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to coated textile fabric used in the manufactureof inflatable devices such as air bags, side air curtains or the like,for vehicle occupant restraint systems. More particularly, the inventionrelates to woven or knitted textile fabrics coated with a plurality ofpolymeric layers that impart superior air holding and heat sealableproperties to the fabric. The polymeric coatings of the invention form abead when heat sealed, thus providing a reinforced heat seal bond thatpermits the manufacture of preformed air holding channels and/or sideair curtains that will withstand the explosive pressure of inflation gaswhen the air bag is deployed.

2. Description of the Related Art

Present restraint systems for automotive vehicles include driver andpassenger side air bags that are instantaneously gas-inflated byexplosion of a pyrotechnic material at the time of a collision toprovide a protective barrier between vehicle occupants and the vehiclestructure.

Much of the impact of a collision is absorbed by the air bag, thuspreventing or lessening the possibility of serious bodily injury tooccupants of the vehicle. Air bags are located, typically, in acollapsed, folded condition housed in the steering wheel, to protect thedriver, and in the dashboard, to protect a passenger seated next to thedriver. Recently, the automotive industry has introduced air bags thatare stored in the back of the front seats or in the rear seats toprotect the cabin occupants in the event of a collision occurring, oneither side of the vehicle. More recently still, another safety featurethat has been made available for passenger vehicles, especially theso-called sport utility vehicles or SUVs includes side-impact protectiveinflatable side air curtains designed to provide a cushioning effect inthe event of side collisions or rollover accidents. These side aircurtains are stored uninflated in the roof of the vehicle and, in theevent of a collision, deploy along the interior side walls of the cabinof the SUV.

Each of these various types of air bags and side air curtains hasdistinct design and physical property requirements, such as gas (air)holding permeability, air pressure and volume control, and punctureresistance. For example, driver side air bags, which inflate and deflatealmost immediately thereafter, must have little or no permeability.Passenger side air bags, on the other hand, require a controlledpermeability. Moreover, all such vehicle air restraint devices must havesuperior packageability and anti-blocking qualities. Packageabilityrefers to the ability of a relatively large device such as an air bag tobe packaged in a relatively small space as, for example, within asteering wheel. Anti-blocking refers to the ability of the device todeploy practically instantaneously without any resistance caused by thematerial sticking to itself, particularly after being stored forrelatively long periods of time before it is deployed. These and otherproperties are determined in large part by the type of fabric used,whether it is knitted or woven, and most importantly, the nature of thecoatings that are used on the fabric.

The air holding capability of side air curtains is critical since thesesafety devices must remain inflated for an extended period of time toprotect passengers in multiple rollovers. Unlike air bags which aredesigned to inflate instantaneously, and to deflate almost immediatelyafter inflation in order to avoid injury to the driver and front seatpassenger, side air curtains used in SUVs, or in ordinary passengervehicles, must be capable of remaining inflated in the range of fromabout three (3) to about twelve (12) seconds, depending upon the size ofthe air curtain and the size and type of vehicle involved. An averagepassenger vehicle would require a side air curtain of from about 60inches to about 120 inches in length as measured along the length of thevehicle. A larger vehicle, such as a minivan, would require an evenlonger side air curtain. The maximum inflation period of a side aircurtain should be sufficient to protect the cabin occupants during three(3) rollovers, the maximum usually experienced in such incidents.

When side air curtains are deployed, they may be subjected to pressureswithin a relatively broad range, depending upon their specific locationor application. For example, air bag deployment pressures are generallyin the range of from about 50 kilopascals (kpa) to about 450 kpa, whichcorresponds generally to a range of from about 7.4 psi (pounds persquare inch) to about 66.2 psi. Accordingly, there is a need for fabricproducts and air bags which can be made to be relatively impermeable tofluids under such anticipated pressures while being relatively light inweight.

One means of improving air holding capability in vehicle restraintsystems has been through coatings such as chloroprene and siliconerubber coatings, applied to the textile (e.g., nylon) substrate. U.S.Pat. No. 5,110,666 discloses a woven nylon substrate coated withpolyurethane to provide the desired permeability and retention ofinflation gas. Nevertheless, wherever coated fabrics are used theproblems of controlling air permeability air pressure and volume remain.Additionally, in the manufacture of air bags in which stitching is usedto form the bag structure, each stitch creates a potential leak thatadversely affects the integrity and air holding capability of the bag,especially when instantaneous deployment of an operative bag isrequired. Insufficiency of adhesion of the coating to the fabricsubstrate also is a serious problem that must be addressed. For example,the smoother the substrate surface, generally the more difficult it isto obtain strong adhesion of the coating material to the substrate. Withsome coatings such as silicone rubber (polysiloxane), radio frequency(RF) heat sealing techniques cannot be used to form the air bag becausethis material will not flow at heat sealing temperatures. In suchinstances, air bags are usually made by stitching, a process whichrequires the addition of an adhesive sealant, ultrasonic weld, RF weldor other type of fusion process in the stitched areas. Even so, asnoted, leakage of air may occur at the stitching, which lessens theprotective capability of the air bag.

There have recently been developed improved polyurethane, acrylic,polyamide and silicone coatings that are coated in layers on the fabricsubstrates. It has been found that adhesion characteristics are greatlyimproved with such layered coatings. Examples of such coated fabrics andmethods of coating such fabrics are disclosed in commonly assignedapplication Ser. Nos. 09/327,243, 09/327,244 and 09/327,245, filed Jun.7, 1999, the disclosures of which are incorporated herein by referenceand made a part of this disclosure.

U.S. Pat. No. 5,363,644 discloses woven or laid structures using hybridyarns comprising reinforcing filaments and lower melting matrixfilaments comprised of thermoplastic polymers to form textile sheetmaterials of adjustable gas and/or liquid permeability. During theformation of textile fabrics in accordance with the disclosure,polyester fibers in the weaves are melted by the application of heat toform textile sheet materials that are stated to have predetermined gasand/or liquid permeability. I have invented a coated textile fabric forair holding-devices in inflatable vehicle restraint systems which can beheat sealed to withstand inflation pressures in a controlled andimproved manner and without stitching.

SUMMARY OF THE INVENTION

It has been found that a textile fabric substrate, when coated with amulti-layered polymeric coating, including a composite coating layer ofpolyurethane polymer and polysiloxane provides an improved heat sealablecoated textile fabric for inflatable vehicle restraint systems.Preferably a suitable adhesion promoter and filler such as epoxy resinis added to the composite coating layer. The composite layer facilitatesthe formation of a sealing bead when heat sealed with a similarly coatedfabric, to provide a reinforced heat seal bond. The exceptional bondingproperties thus obtained permit the manufacture of an air bag or sideair curtain with preformed air holding channels that will be able towithstand the pressure of inflation gas without the need for stitching.

The coatings of this invention can be applied directly onto the textilesubstrate itself or indirectly by transfer coating to a coated carriersheet. Multiple reinforced seals can be generated with a bead effect bymeans of a RF (radio frequency) heat sealing bar having predesigned beadcavities in the die. During the heat sealing process the components thattogether comprise the composite coating layer of the invention flow atdifferent temperatures, thus creating a bead in the preformed die cavitydesign. In this process, when heat is applied in a predeterminedtemperature range, the polyurethane polymer flows into the preformedcavity of the die, thus creating a bead, while the polysiloxane does notflow at the heat sealing temperatures utilized. Vulcanization of thepolysiloxane takes place at the time of, or immediately after formationof the bead to bond the polymeric layers together. In addition to itsmajor components of polyurethane and polysiloxane, in the preferredembodiment the composite coating layer would also include an adhesionpromoter and filler such as an epoxy resin and may also includesolvents, fillers and an ultraviolet light absorber to indicate wherethe flow of the seal bond is taking place for purposes of inspectionunder an ultraviolet light. Other additives which act as adhesionpromoters and fillers which are comparable to epoxy resin are alsocontemplated.

A method of producing a coated textile fabric for an air holding devicein a vehicle restraint system is also disclosed, which comprises takinga base textile fabric having first and second surfaces, coating a firstlayer of an adhesive polyurethane onto the first surface of the textilefabric, and drying the first layer at an elevated temperature to form afirst coating layer. The method further comprises coating a compositecoating layer which includes a polyurethane and a polysiloxane onto thefirst coating layer and drying the composite coating layer at anelevated temperature to form a second coating layer. The method furthercomprises coating a third polyurethane layer onto the second compositecoating layer and drying the third polyurethane layer.

A heat sealing die for sealing coated air bag fabrics is also disclosed,which comprises a heat sealing bar having a generally planar surface,and a combination of straight and arcuate cavities in the planarsurface. The cavities are positioned in predetermined relative positionsand orientations to form sealing beads on the coated air bag fabrics.The cavities each have an arcuate cross-sectional configuration to formsealing beads having corresponding cross-sectional configurations.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described hereinbelow withreference to the drawings, wherein:

FIG. 1 is a cross-sectional view of a typical coated base fabric of theinvention;

FIG. 2 is a cross-sectional view of a typical coated base fabric of theinvention with an additional layer coated on the opposite side of thebase fabric;

FIG. 3 is an exploded perspective view from below, of the heating dieswith the fabrics and coating materials positioned for heat sealing inaccordance with the invention;

FIG. 4 is a partial perspective view from below, of one form of heatingdie with preformed bead cavities;

FIG. 5 is a partial perspective view from below, of an alternative formof heating die having alternative preformed bead cavities; and

FIG. 6 is a cross-sectional view of the heating die of FIG. 4 in theclosed position with a mating flat surface heating die, illustrating thecoated fabrics of the invention heat sealed together with a pair ofbeads formed by the dies.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a coated textile fabric that can bejoined by heat sealing to form an inflatable air holding device such asan air bag or a side air curtain, for a vehicle restraint system. Theair holding device can be produced by coating such fabrics with multiplepolymeric layers, including a composite coating layer of polyurethanepolymer and polysiloxane, with the preferred addition of an epoxy resin,to produce a product that can be joined by heat sealing with a similarlycoated fabric. The heat seal bonding properties of these coated fabricsare greatly enhanced by the formation of a bead which reinforces theheat seal and permits the production of side air curtains having variouspreformed shapes without the use of stitching. In forming these coatedfabrics, a base fabric substrate is first coated on a first side with aprime coat of an adhesive polyurethane layer to enhance adhesion ofsubsequent layers and to control the penetration of a second compositecoating layer into the textile. The fabric is thereafter coated with anon-sticking polyurethane top coat.

The composite coating layer of the invention comprises a mixture ofpolymeric polyurethane and polysiloxane, with the preferred addition ofan epoxy resin which is introduced to promote heat sealing and adhesionof the mixture to polyamide, polyester or other synthetic polyolefinfibers. The polyurethane polymer in the composite mixture will flow atheat sealing temperatures of from about 380° F. to 420° F., while thepolysiloxane component will not flow at these temperatures. As a result,the polyurethane polymer will flow into the die cavity formed when theheat sealing bar is closed, while the polysiloxane, which isincompatible with the polyurethane, and does not flow at suchtemperature, will cross-link or vulcanize. This produces a polyurethanereinforcing bead in the heat seal bond, while the vulcanizedpolysiloxane prevents the polyurethane from flowing into the textilesubstrate. A catalyst is added to the polymeric composite mixture topromote vulcanization of the polysiloxane at a temperature of from about375° F. to about 400° F.

The polysiloxane is resistant to heat UP to a temperature of about 600°F. after vulcanization.

The polyurethane prime coat is comprised of from about 20 to about 50weight percent polyurethane, with the remainder of the formulation beingsolvent, biocide and ultraviolet stabilizer. The polymeric compositecompound used for the composite layer is comprised of from about 40 toabout 100 weight percent polyurethane, from about 5 to about 25 weightpercent polysiloxane, from about 5 to about 25 weight percent epoxyresin, with the remainder of the formulation being comprised of solvent,biocide and ultraviolet stabilizer. The polyurethane topcoat, or finishcoat, is comprised of from about 15 to about 35 weight percent ofpolyurethane.

The opposite (or second) side of the fabric may be coated or uncoated.In the coated embodiment, the second surface coating may be eitherpolyurethane or polysiloxane based. The polyurethane topcoat iscomprised of from about 40 to about 100 weight percent polyurethane,from about 5 to about 25 weight percent epoxy resin, with the remainderof the composition being comprised of biocide, ultraviolet stabilizers,fillers and adhesion promoters. The polysiloxane coating is comprised offrom about 5 to about 25 weight percent polysiloxane and from about 5 toabout 25 weight percent epoxy resin filler or other suitable fillers oradhesion promoters.

Either natural or synthetic knit, woven or non-woven fabric can beemployed as the textile substrate, with substrates of polyamide orpolyester fibers being preferred. Woven nylon as the fabric substrate isespecially preferred. Any denier size, fiber shape or weavingconfiguration can be employed to advantage in the invention. The shapeor configuration of the air holding restraint device utilized in thesystem will depend upon its ultimate location in the vehicle. Forexample, driver or passenger side air bags will generally be elliptical,spherical or circular in shape, while side air curtains will generallybe rectangular or oval in configuration.

The direct or transfer coating of the textile substrate with layers ofpolymeric coating material takes place on a coating line that hasmultiple coating stations with multiple dryers in sequence. In thedirect coating process, the fabric substrate is heat-set and stabilizedprior to applying the first (prime) polyurethane coating layer bypassing it through an oven at a temperature of from about 250° F. toabout 400° F. Thereafter, the fabric is coated in accordance with theinvention. In the transfer coating application, the various coatingmaterials are first transferred by laminating the multiple layersthereof to a carrier sheet and then laminating the textile or knitsubstrate thereto.

In one embodiment of the present invention, as shown in FIG. 1, a fabricsubstrate 10 is first coated on its upper or top surface 12 with anadhesive polyurethane layer 14, referred to as a prime coat or adhesivecoat. The adhesive coat serves to adhesively bond the filaments of thetextile substrate so they do not comb or unravel. The polyurethane usedin the prime or adhesive layer 14 can be selected from among thearomatic or aliphatic polyether or polyester polyurethanes and,preferably, from among those having a solids content of from about 20%to about 75% by weight. These types of polymeric polyurethanes providegood adhesion to nylon and satisfactory hydrolysis, i.e. resistance tobreakdown under ambient storage conditions, to insure that the air bagor side air curtain will be ready for use when deployed.

Preferably, the prime coat layer 14 covers the entire surface 12 of thefabric 10. Alternatively, it can be applied as a partial coatingdesigned to coincide with a particular area of the fabric as in a designfor air channels for side air curtains. etc. In addition, variouspatterns and coating weights can be employed to obtain the desired levelof air permeability in the finished air bag.

The prime coat layer 14 is dried in an oven at from about 225° F. toabout 450° F. for about 1.5 to about 3.0 minutes, while advancing thefabric at a speed of from about 300 yards per hour to about 3,000 yardsper hour, with 1,200 yards per hour being preferred. In this phase ofthe process the polyurethane layer and the nylon substrate form across-linked polymer chain, thus securely adhering the adhesive layer tothe base fabric substrate.

At a second coating station, a composite coating layer 16 is depositedand coated onto the prime coating layer 14. The composite coating layer16 is comprised of from about 25% to about 100% solids by weight of anaromatic or aliphatic polyether or polyester polyurethane andpolysiloxane, with an epoxy resin preferably included in the mixture.Optionally, depending upon the chemical and physical properties soughtto be introduced into the air bag, additional materials are added to thepolymeric composite compound as, for example, flame proofing agents,such as aluminum trihydrate, melanine, bromine, or antimony trioxidemildew prevention agents such as BP50 by Morton Thiokol; ultraviolet andozone resistant agents, such as Tinuvin 765® by Ciba Geigy; ultravioletabsorbent materials and Intratherm dyes. During the heating process, thecomposite coating layer 16 reacts with and chain extends with the primecoat layer 14 to establish a homogeneous composite layer 15 whereby bothlayers become cross-linked or bonded together. The coating weight of thehomogeneous composite layer 15 is within the range of from about 0.5ounces per square yard to about 14 ounces per square yard, with about3.5 ounces per square yard being preferred. The coated fabric is thendried in an oven maintained at an elevated temperature of from about350° F. to about 450° F.

After the composite coating layer 15 is applied, a third layer ortopcoat layer 1 S of an aliphatic or aromatic polyether or polyesterpolyurethane is coated onto the homogeneous composite layer 15. Topcoatlayer 18 is designed to prevent blocking or self-sticking of the air baglayers to each other when the air bag is in its collapsed, foldedcondition during storage and, later, upon deployment. The coating weightof the topcoat layer is from about 0.2 to about 3.0 ounces per squareyard with a coating weight of about 0.5 ounces per square yard beingpreferred. The topcoat layer is heated at an elevated temperature offrom about 250° F. to about 400° F. for about 1.5 to from about 3.0minutes in an oven, during which time it cross-links with thehomogeneous composite layer 15.

The laminated structure shown in FIG. 1 typically forms a panel of anair bag or a side air curtain after die cutting into the desiredconfiguration by the air bag manufacturer. A complementary laminatedstructure, similar to the structure of FIG. 1, forms the opposite panelof the air bag or side air curtain. In accordance with the presentinvention, the two panels are sealed together about their peripheries oralong a predesigned configuration to form air channels for side aircurtains by radio frequency (RF) heat sealing, hot air sealing orultrasonic sealing at from about 10 to about 80 megahertz, and at fromabout 250° F. to about 450° F., with RF heat sealing being preferred.Sealing in this manner serves to better control the air permeability ofthe air bag while maintaining its integrity against air leakage, sincethe inherent leakage problems associated with conventional closing bystitching or sewing are avoided. Employing an RF heat sealing system isespecially important in the manufacture of air filled tubular side aircurtains since air must be held in these structures for longer periodsof time than with a conventional air bag. Such curtains must open within2 to 3 milliseconds of impact and must stay inflated for about 3 toabout 12 seconds after deployment in the case of multiple rollovers,e.g. three rollovers, in a single incident.

As shown in FIG. 3, the coated fabrics 30 and 40 are aligned within theRF heat sealing bars 1 and 2 in a position such that their multi-layeredcoating surfaces 3 and 4 face each other. When heat sealing dies 1 and 2are closed and heat is applied, coated fabrics 30 and 40 are heat bondedtogether at their points of contact. In addition, predesigned heat sealcavities 4 and 5 in heat seal bar die 1 provide locations for beadformation in the heat sealing process. Heat seal bar 2 has a flat innersurface (not shown) which provides additional pressure in the beadformation. The result, as shown in FIG. 6, is a joining of coatedfabrics 30 and 40 (individual coating layers not shown) with bead formedat cavities 4 and 5 in the heat seal bar die 1.

One type of straight line bead design is shown in FIG. 4 which hasparallel straight line bead cavities 4 and 5. A die 7 having analternative type of bead design is shown in FIG. 5, which includes acombination of straight line bead cavities 4 and 5 and a wavy orundulating bead cavity 6. While the bead cavities shown in FIG. 4 arepreferably of a width and depth of about ⅛″ and those of FIG. 5 arepreferably of a width of about 0.142″ and a depth of about ⅛″ in theprocess and equipment described herein, the bead cavities can be of anyappropriate width and depth sufficient to create a strong reinforcingseal in a particular application. If desired, these and other heat sealbead cavities may be joined together as, for example, interconnectingcavities in a predesigned continuous arrangement to form closed airchambers for an air bag; or a side air curtain or other type of air bagdevice.

In another embodiment of the present invention, as shown in FIG. 2, theupper or outer surface 12 of fabric 10 is coated with the same coatinglayers 14, 16 and 18 as shown in FIG. 1. However, in this alternativeembodiment, the bottom surface 20 of fabric substrate 10 has anadditional layer of polymeric material 22 coated thereon. Polymericlayer 22 can be comprised of a non-sticking material such aspolysiloxane or, where an adhesive or sticking application is required,an adhesive polyurethane. The coated fabric is dried in an oven at atemperature of from about 275° F. to about 450° F. at which temperaturethe polysiloxane coating vulcanizes with the textile substrate. Thecoating weight of the polymeric polysiloxane or polyurethane layer 22 onthe bottom surface 20 of the textile fabric substrate is from about 0.5ounces per square yard to about 5.0 ounces per square yard, with 1.2ounces per square yard being preferred. This coating layer providesadded protection to the textile fabric against the high temperaturesencountered upon inflation with hot gases.

While the preferred embodiments of the invention have been illustratedand described, using specific terms, such description has been forillustrative purposes only, and it should be understood that changes andvariations may be made thereto without departing from the spirit andscope of the invention which is defined by the claims appended hereto.

What is claimed is:
 1. A method of producing a coated textile fabric foran air holding device in a vehicle restraint system, which comprises:(a) taking a base textile fabric having first and second surfaces; (b)coating a first layer of an adhesive polyurethane onto said firstsurface of said textile fabric and drying said first layer at anelevated temperature to form a first coating layer; (c) coating acomposite coating layer comprising a polyurethane and a polysiloxaneonto said first coating layer and drying said composite coating layer atan elevated temperature to form a second coating layer; (d) coating athird polyurethane layer onto said second composite coating layer; and(e) drying said third polyurethane layer.
 2. The method of claim 1wherein said composite coating layer is comprised of a polyurethane, apolysiloxane and an epoxy resin.
 3. The method of claim 1 wherein saidtextile fabric is selected from the group consisting of polyesters,polyamides and other synthetic fibers.
 4. The method of claim 1 whereinsaid textile fabric is selected from the group consisting of knitted,woven and non-woven fabrics.
 5. The method of claim 1 wherein saidtextile fabric is a woven nylon fabric.
 6. The method of claim 1 whereinsaid first coating layer is selected from the group consisting ofaromatic or aliphatic polyester polyurethanes and aromatic or aliphaticpolyester polyurethanes.
 7. The method of claim 1 wherein said firstcoating layer has a solids content of from about 20% to about 75% byweight.
 8. The method of claim 1 wherein said first coating layer isdried in an oven at a temperature of from about 225° F. to about 450° F.for about 1.5 to about 3.0 minutes, while advancing the fabric at aspeed of from about 300 yards per minute to about 3,000 yards per hour.9. The method of claim 2 wherein the composite coating layer has asolids content of from about 25% to about 100% by weight and a coatingweight of from about 0.5 ounces per square yard.
 10. The method of claim6 wherein said composite coating layer is dried in an oven at atemperature of from about 350° F. to about 450° F.
 11. The method ofclaim 2 wherein a third layer or topcoat is dried in an oven at atemperature of from about 250° F. to about 400° F. for about 1.5 toabout 30 minutes to cross-link the topcoat layer with the PES compositelayer.
 12. The method of claim 6 wherein the third layer or topcoatlayer has a coating weight of from about 0.2 to about 2.0 ounces persquare yard.
 13. A method of producing a coated textile fabric for anair-holding vehicle restraint system, which comprises: (a) taking atextile fabric having first and second surfaces; (b) coating a firstlayer of adhesive polyurethane on said first surface of said textilefabric; (c) coating a second layer comprising a composite of apolyurethane, an epoxy and a polysiloxane onto said first coating layer;(d) coating a third polyurethane layer onto said composite coatinglayer; and (e) coating a polymeric polyurethane layer onto said surfaceof said textile fabric.
 14. The method of claim 13 wherein saidpolymeric polyurethane coating layer is dried in an oven at atemperature of from about 275° F. to about 450° F. to vulcanize saidpolyurethane with the textile fabric.
 15. The method of claim 13 whereinsaid polymeric polyurethane coating layer has a coating weight of fromabout 0.5 ounces per square yard to about 5.0 ounces per square yard.